In recent years, numerous food poisoning outbreaks involving various pathogens, along with the increasing concern about the preservation of minimally processed foods, have spurred growing awareness of the importance of food safety. This has prompted new approaches, on the one hand to inhibit food-borne pathogens, and on the other hand to prolong the shelf life of food products. In particular, there has been an increasing interest in the antimicrobial activity of lactic acid bacteria. Lactic acid bacteria have been used for centuries in the fermentation of foods, not only for flavor and texture development, but also because of their ability to produce antimicrobial compounds, which prevent the growth of spoilage and pathogenic microorganisms (De Vuyst and Vandamme 1994).
Among the antimicrobial compounds produced by lactic acid bacteria, bacteriocins are defined as proteinaceous compounds, which kill closely related bacteria (Tagg et al. 1976). Based on the observed structural characteristics, bacteriocins have been grouped into three classes. Class I (lantibiotics) and Class II (small, heat stable, non-lanthionine containing peptides) are the most abundant and thoroughly studied. In particular, the lantibiotics have attracted much attention in the last decade, because of the success of the well-characterized lantibiotic nisin as a food preservative. Indeed, the commercial exploitation of bacteriocins to date is mainly restricted to the food applications of nisin, the prototype lactic acid bacterium bacteriocin first discovered in 1928 by Rogers.
It is generally accepted that bacteriocins produced by lactic acid bacteria kill phylogenetically closely related bacteria, even though many characterized bacteriocins concur with this definition. For instance, it has become apparent that some have a broad host-range, inhibiting many different species and/or genera (McAuliffe et al. 2001). Indeed, both nisin and pediocin display a broad inhibitory spectrum. Due to this broad inhibitory spectrum and its lactic acid bacterium origin, until today nisin is the only bacteriocin used and approved in several foods worldwide.
There is however a growing need for new thermostable food grade bacteriocins which show activity in a broad pH range against a broad spectrum of microorganisms.
So far, streptococcal lantibiotics have been mainly isolated from oral streptococci. These bacteria are commonly found in the oral cavity and upper respiratory tract of humans and animals, although they may be isolated from almost any type of clinical specimen as well (Hardie 1986). Crossing the borders of pathogenicity, it is obvious that lantibiotic-producing oral streptococci have no chance to be used as such in food applications.
In spite of several problems concerning bacteriocin production in food environments still need to be addressed, the use of bacteriocin-producing cultures in food is of considerable advantage over using purified bacteriocin preparations.
Therefore it is one of the aims of the present invention to provide novel bacteriocins from safe microorganisms and use both said bacteriocins and said bacteriocin-producing strains in food industry.